Variation with h of the ratio between the solid angle of the radiation which reaches the equatorial plane and the same solid angle as it would come out in a flat spacetime, in the assumption that the disc extends up to 1000r_g and for three values of the BH spin (solid line: a=m; dotted line: a=0.5m; dashed line: static BH). The photons' deflection towards the disc, i.e. the anisotropy of the illuminating radiation field, strongly increases with decreasing primary source height. See Martocchia & Matt (1996), and Martocchia (2000) for details.

Figure 2:

Disc emissivity (in arbitrary units) vs. radius (in units of r_g) for a source located at h=3r_g (solid line) and h=4r_g (dashed line) in a maximally spinning BH metric. The lower, straight dotted line corresponds to a power law with ß ~   4.

Figure 3:

Fe  Kα profiles computed with the XSPEC routine kerrspec (Martocchia 2000), using respectively a power-law emissivity with ß=4 (solid line) and a lamp-post emissivity with h=3r_g  (dashed line). All other parameters have been fixed to the best-fit values  found by Wilms et al. (2001). Differences between the two plotted models are clearly too small to be detectable by XMM.